{
 The NetGetDCName function returns the name of the primary domain controller (PDC).
 It does not return the name of the backup domain controller (BDC) for the specified domain.
 Also, you cannot remote this function to a non-PDC server.
 Windows 2000/XP: Applications that support DNS-style names should call the function.
 Domain controllers in this type of environment have a multi-master
 directory replication relationship.
 Therefore, it may be advantageous for your application to use a DC that is not the PDC.
 You can call the DsGetDcName function to locate any DC in the domain;
 NetGetDCName returns only the name of the PDC.
}
type
 EAccessDenied = Exception;
 EInvalidOwner = Exception;
 EInsufficientBuffer = Exception;
 ELibraryNotFound = Exception;
 NET_API_STATUS = Integer;
const
 NERR_Success = 0;
var
 NTNetGetDCName: function (Server, Domain: pWideChar; var DC: pWideChar): NET_API_STATUS; stdcall;
 NTNetGetDCNameA: function (Server, Domain: PChar; var DC: PChar): NET_API_STATUS; stdcall;
 NTNetApiBufferFree: function (lpBuffer: Pointer): NET_API_STATUS; stdcall;
procedure NetCheck(ErrCode: NET_API_STATUS);
begin
 if ErrCode <> NERR_Success then
 begin
  case ErrCode of
  ERROR_ACCESS_DENIED:
  raise EAccessDenied.Create('Access is Denied');
  ERROR_INVALID_OWNER:
  raise EInvalidOwner.Create('Cannot assign the owner of this object.');
  ERROR_INSUFFICIENT_BUFFER:
  raise EInsufficientBuffer.Create('Buffer passed was too small');
  else
  raise Exception.Create('Error Code: ' + IntToStr(ErrCode) + #13 +
  SysErrorMessage(ErrCode));
  end;
 end;
end;
function GetPDC(szSystem: string): string;
 { if szSystem = '' return the PDC else return DC for that domain }
const
 NTlib = 'NETAPI32.DLL';
 Win95lib = 'RADMIN32.DLL';
var
 pAnsiDomain: PChar;
 pDomain: PWideChar;
 System: array[1..80] of WideChar;
 ErrMode: Word;
 LibHandle: THandle;
begin
 Result := '';
 LibHandle := 0;
 try
  if Win32Platform = VER_PLATFORM_WIN32_NT then
  begin
  ErrMode := SetErrorMode(SEM_NOOPENFILEERRORBOX);
  LibHandle := LoadLibrary(NTlib);
  SetErrorMode(ErrMode);
  if LibHandle = 0 then
  raise ELibraryNotFound.Create('Unable to map library: ' +
  NTlib); @NTNetGetDCName := GetProcAddress(Libhandle, 'NetGetDCName');
  @NTNetApiBufferFree := GetProcAddress(Libhandle,
  'NetApiBufferFree');
  try
  if szSystem <> '' then
  NetCheck(NTNetGetDCName(nil, StringToWideChar(szSystem, @System, 80), pDomain))
  else
  NetCheck(NTNetGetDCName(nil, nil, pDomain));
  Result := WideCharToString(pDomain);
  finally
  NetCheck(NTNetApiBufferFree(pDomain));
  end;
  end
  else
  begin
  ErrMode := SetErrorMode(SEM_NOOPENFILEERRORBOX);
  LibHandle := LoadLibrary(Win95lib);
  SetErrorMode(ErrMode);
  if LibHandle = 0 then
  raise ELibraryNotFound.Create('Unable to map library: ' +
  Win95lib); @NTNetGetDCNameA := GetProcAddress(Libhandle, 'NetGetDCNameA');
  @NTNetApiBufferFree := GetProcAddress(LibHandle, 'NetApiBufferFree');
  try
  if szSystem <> '' then
  NetCheck(NTNetGetDCNameA(nil, PChar(szSystem), pAnsiDomain))
  else
  NetCheck(NTNetGetDCNameA(nil, nil, pAnsiDomain));
  Result := StrPas(pAnsiDomain);
  finally
  NetCheck(NTNetApiBufferFree(pAnsiDomain));
  end;
  end;
 finally
  if LibHandle <> 0 then
  begin
  FreeLibrary(Libhandle); // free handle if it has been allocated
  end;
 end;
end;
// Example call, Beispielaufruf:
procedure TForm1.Button1Click(Sender: TObject);
begin
 try
  Screen.Cursor := crHourGlass;
  label1.Caption := GetPDC('');
 finally
  Screen.Cursor := crDefault;
 end;
end;